The invention relates to a hingeless rotor, especially for helicopters whereby the rotor has at least two rotor blades each of which is secured through a connecting element to the rotor hub. Each connecting element functions as a flapping hinge, as a lead-lag hinge, and as a torsion hinge. Such hingeless rotors are suitable for use as lifting rotors or as tail rotors in helicopters or rotary wing aircraft.
German Patent Publication (DE-AS) No. 1,531,375 discloses a rotor in which each rotor arm comprises a blade angle sleeve in which a blade root sleeve is rotatably supported. The arrangement is such, that the blade root sleeve can perform the blade angle movements caused through a control rod. A neck section of the rotor blade is secured to the blade root sleeve and such neck section merges into the blade root. The neck section forms an integral or one piece extension of the carrier bar of the wing section of the rotor blade. The neck section is so constructed that it is flexible in the lead-lag direction and in the flapping direction while being simultaneously stiff against torsion loads. The cross-section of the neck section is so constructed that the bending loads in the lead-lag direction and in the flapping direction are substantially equal to each other. In this prior art rotor it is necessary to provide a bearing which is formed by the blade angle bearing sleeve and by the blade root sleeve in order to permit the blade angle movements.
Another prior art rotor has been constructed without such bearings so that the rotor is entirely hingeless. In order to realize such a construction, a leaf spring type connecting element is clamped to the rotor hub at one of its ends while the other end of the connecting element merges into the blade root. The desired load stiffness or flexibility in the flapping direction is achieved on the one hand by the leaf spring action of the connecting elements formed as a laminated body. On the other hand, such load stiffness is also facilitated by the partially elastic clamping of the connecting element at its end adjacent the rotor hub. Due to this clamping and due to the flexibility of the leaf spring, it is possible to perform the blade angle movement in response to a control lever forming an integral part of the blade root zone. A connecting element of the just described type is disclosed in U.S. Pat. No. 3,880,551. However, this type of arrangement has the disadvantage that the stiffness of the connecting element in the lead-lag direction and in the direction of the blade angle or torsion movement is relatively large. Additionally, the elastic clamping of the connecting element adjacent to the rotor hub is rather expensive if it can be realized in practice at all.